A mother and son involved in a serious assault on a man were sentenced in the Invercargill District Court yesterday.

Jacqueline Marline McKenzie, 42, and her son Dylan Takitimu-McKenzie, 21, appeared before Judge Kevin Phillips on charges of aggravated robbery and injuring with intent to injure on August 20, 2011.

The mother was sentenced to eight months' home detention and 250 hours' community work, and her son was sentenced to two years and six months' jail.

The pair pleaded guilty to the offences at their trial earlier this year. The Crown said the son was the principal offender while the mother was a party to it.

Judge Phillips said the offending defied belief. He said a young drug dealer, who was related to the pair, was having difficulty with a person she had supplied drugs to and called on the son to scare him.

He told her he would deal with it at the weekend and was promised a reward in cannabis, the judge said.

The son said he had had a week from hell and would take it out on the person, Judge Phillips said.

About 11.30pm on August 20, 2011, the son and others were in a vehicle being driven by the mother, which stopped around the corner from where the victim lived.

The pair and another person got out of the car after a text message was sent to the victim to get him outside.

The son approached the victim and hit him in the head with a hammer twice before people stomped and kicked him while he was on the ground. Another person put a chain around the victim's neck and tightened it. The victim was told to empty his pockets and the son struck him again, knocking him unconscious.

When spoken to by police, the son admitted punching the victim but denied using the hammer or kicking him. The mother said she was in Christchurch and played no role.

Judge Phillips said the victim was terrified and distraught over the offending and had since had trouble with his memory.

The son's lawyer, Roger Eagles, said his client, who was 19 at the time, was remorseful. He had a $5000 vehicle he was willing to sell to put towards compensation. The mother's lawyer, John Westgate, said she regretted what happened that night.